How to Calculate Vancomycin Dosing Interval

Introduction

Vancomycin is typically administered as an intravenous infusion. The dosing interval depends on several factors including the patient's weight, renal function, and the specific indication for treatment. The standard dosing regimen is usually every 12 hours, but this can vary based on individual patient characteristics.

The primary goal of vancomycin dosing is to maintain serum concentrations within the therapeutic range (15-20 mcg/mL) to ensure effective antibacterial activity while avoiding toxic levels (>30 mcg/mL).

Vancomycin Dosing Formula

The standard vancomycin dosing formula is based on the patient's weight:

For patients with impaired renal function, the dosing interval may need to be adjusted to maintain therapeutic levels.

Step-by-Step Calculation

1. Determine the patient's weight in kilograms.
2. Calculate the initial dose: 15 mg/kg (maximum 1500 mg).
3. Calculate the loading dose: 25 mg/kg (maximum 2000 mg).
4. Administer the loading dose over 30-60 minutes.
5. Administer the initial dose over 30-60 minutes.
6. Continue dosing every 12 hours unless adjusted for renal function.

Key Factors Affecting Dosing

Several factors influence vancomycin dosing:

• Patient Weight: Dosing is weight-based to ensure appropriate distribution.
• Renal Function: Impaired renal function requires more frequent dosing.
• Hepatic Function: Liver disease may affect drug metabolism.
• Concomitant Medications: Other drugs may interact with vancomycin.

Practical Examples

Example 1: Standard Dosing

For a 70 kg patient:

• Initial dose: 15 mg/kg × 70 kg = 1050 mg
• Loading dose: 25 mg/kg × 70 kg = 1750 mg
• Dosing interval: 12 hours

Example 2: Renal Impairment

For a 60 kg patient with CrCl <50 mL/min:

• Initial dose: 15 mg/kg × 60 kg = 900 mg
• Loading dose: 25 mg/kg × 60 kg = 1500 mg
• Dosing interval: 8 hours (adjusted for renal function)